Speaker
Description
The simultaneous record of photons with at least three telescopes not only allows traditional two-photon correlations between pairs of telescopes, but also to explore three-photon correlations in the telescope triangle. Such measurements in principle enable measurements of the (cosine of the) closure phase, the sum of the interferometric phases in the triangle, and by that retrieve at least parts of the phase information that is inaccessible in intensity interferometry otherwise.
A major caveat is that the three-photon signal is usually significantly smaller than the two-photon signals, and necessary observation times for sensitive closure phase measurements seem yet unreasonable with the current generation of intensity interferometers. For future telescope arrays, however, the closure phase is thought to improve the image reconstruction quality.
The H.E.S.S. Intensity Interferometer performed simultaneous measurements with three telescopes in 2023. Even though the measurements are lacking sensitivity for extracting closure phase information, they are suitable for getting familiar with the concept of three-photon correlations and closure phase measurements in intensity interferometry.
In this talk we present the results of three-photon correlation measurements of two stellar systems - to our knowledge the first astrophysical three-photon correlation measurements. We introduce an analysis algorithm on how to in principle extract closure phase information from the data, and show a proof-of-concept laboratory measurement using pseudo-thermal light with large coherence times, where the cosine of the closure phase is conveniently detectable.
